The process of electroerosive wire-cutting generally makes use of a continuous wire electrode composed of, say, brass or copper, and having a thickness ranging between 0.05 and 0.5 mm. The wire electrode is axially transported continuously along a given continuous guide path from a supply unit to a takeup unit through a workpiece disposed in a predetermined cutting zone. The cutting zone is commonly defined by a pair of cutting guide members which support the wire electrode across the workpiece. Wire traction and braking means allow the continuous wire to be tightly stretched between the supply and takeup units and to be axially driven between the cutting guide members while linearly traversing the workpiece, thus, presenting the continuously renewed electrode surface juxtaposed in a cutting relationship with the workpiece across a machining gap. The latter is flushed with a machining liquid medium supplied from one or more nozzles and is also electrically energized with an electric current which is passed between the wire electrode and the workpiece to electroerosively remove material from the latter. The cutting process may be performed in any of various electroerosive machining modes. In electrical discharge machining (EDM), the machining liquid medium is a dielectric liquid and the electric current is supplied in the form of a succession of electrical pulses. In electrochemical machining (ECM), the liquid medium is a liquid electrolyte and the machining current is a high-amperage continuous or pulsed current. In electrochemical-discharge machining (ECDM,) the machining medium has both electrolytic and dielectric character and the machining current preferably is applied in the form of pulses which facilitate the production of electrical discharges through the liquid medium.
As the electroerosive material removal proceeds, the workpiece is displaced relative to the wire electrode transversely to the axis thereof. This allows the wire electrode to advance transversely to the workpiece and consequently a cutting slot to be formed behind the advancing wire electrode. The continuous relative displacement along a preselected path results in the formation of a desired contour corresponding thereto and defined by this cutting slot in the workpiece.
In performing the electroerosive wire-cutting process, heretofore the cutting zone has been conveniently disposed in the air or like gaseous environment, and a nozzle is used to deliver the machining liquid medium to the cutting gap. The machining liquid is conveniently a water medium which may be ionized or deionized to various extents to serve as a desired electroerosive machining medium. It is desirable to keep the machining gap flushed with a sufficient volume of the cutting liquid and traversed thereby at a suitable rate to allow the electroerosive action to continue with stability, the cutting chips and other gap products to be carried away with smoothness, and the wire electrode to be cooled with effectiveness. In the conventional arrangement in which the cutting zone or nozzle is exposed to the air, however, the machining liquid, due to a pressure drop caused when it leaves the nozzle, tends to splash away so that most of it flows out without ever being forced through the narrow machining-gap spacing provided between the thin wire electrode and the workpiece. When the delivery of the liquid medium to the machining gap is insufficient or the machining gap is incompletely filled with the liquid medium, there develop gaseous discharges therein which impair the electroerosive process and removal of the gap products and eventually cause breakage of the wire electrode due to excessive heat which then develops or due to an insufficient cooling of the wire electrode. An uncontrolled increase of the pressure of the liquid trained towards the machining gap in the workpiece disposed in the air environment in an attempt to ensure full delivery of the machining liquid into the cutting zone will bring about an uncontrolled deflection or vibration of the wire electrode which again impairs the cutting stability. In short, there have been undue limitations of cutting stability and efficiency which accrue from the conventional gap flushing technique in the electroerosive wire-cutting process.